A continuing goal is development of methods for studying structural, and transport properties of complex biological media. During the past year we continued theoretical investigations of various aspects of photon migration in turbid biological media, have initiated experimental correlates of those theories, extended the use of dynamic light scattering to probe blood flow in tissue microvasculature, developed methods for using quasielastic light scattering to study the properties of gels and polymer lattices, and performed analyses of neutron scattering measurements of the structure of core constituents of biological vesicles. A major accomplishment has involved application of random walk theory to timeresolved in vivo optical absorption spectroscopy of biological tissue (with R. Bonner and G. H. Weiss). This work underlies attempts to develop novel noninvasive techniques to measure cerebral blood oxygenation (B. Chance, et al). Analysis of the time course of the light exiting a tissue after application of a photon pulse has been shown to yield information about tissue scattering and absorption parameters. Preliminary experimental studies (with B. Chance) have verified some of the theoretical inferences, and protocols are being developed to enable investigation of effects of superficial layers (such as the skull) which have different scattering and absorption properties. We also analyzed other aspects of the way that optical path length influences remote optical sensing of biological tissue.